重水中, 数種の脂肪酸による4-メチルピリジンの水素-重水素交換反応

抄録

Hydrogen-deuterium exchange of 4-methylpyridine (1b) has been studied by using fatty acid RCO₂H (R=C₁C₁₀) as a catalyst in D₂O at 120°C. The reaction mixture is homogeneous in the case of R=C₁C₃, and heterogeneous with R=C₄C₁₀. The conversion (or contents) -time curves show typical stepwise reactions (d₀→d₁→d₂→d₃). The rate increases with the increase in the concentration of the acids. The conversion decreases and increases, respectively, in the cases of R=C₅C₁₀ and R=C₁C₃ with increasing the concentration of the substrates. The mode of the valeric acid catalyzed reaction (R=C₄) is an intermediate between the two groups above. The reactivity is in the order of 2-methylpyridine (1a) < (1b) in the case of R=C₁C₆, but, (1a) > (1b) with R=C₇C₁₀. From the above observations, a possible mechanism involving protonation and rate-determining attack of free base or carboxylate ion is proposed and discussed by assuming an ion pair model.